Telephonic electrode and method of constructing same



April 28, 1925. 1,535,276

F. L. WHITAKER TELEPHONIC ELECTRODE AND METHOD OF CONSTRUCTING SAMEFiled June 11. 1921 Qwuwtoz Patented Apr. 28, 1925.

outrun; stares;

FRANK L. WHITAKER, OE OLNEY,- ILLINOIS.

TELEPHONIC'ELECTRODE-AND IVIETHOD OF CONSTRUGTING SAME;

Application filed June 11, 1921. Serial No. 476,?95.

To all whom c't may concern Be it known that I, FRANK .L. Vnrrnnnn v acitizen of the United States, residlngz at, ()lney, in the countyofr'Rich-lan'd and State;

In the usuallconstruction ofimicrophonic transmitters the variabletransmlsslon unit comprises one or more vibratory electrodes inelectrical contact with a loose granular, conducting substance, such forexample as carbon, interposed between them andvaris able in theresistancewhich it affords to the passage of: the electric current inratiov to the degreeto whichit is compressed by thew vibration of theelectrodevbetween which it is interposeda Suclr a variable resistanceunit; however presents the disadvantage that the loose granularsubstance is liable to be compacted by the smooth surfaces of theelectrodes thus detracting from; the efliciency ofthe' unit, orthegranular substance:

ismliable tobecome displaced with a like resnlti presentinvention'isctherefore to provide, in a variable resistance unit, anelectrode differing from the ordinary smoothly surfaced electrodeusually employed in that provision is made for a more intimate contactbetween its surface and theparticles of the granular resistancesubstance of the unit, the elec trode being furtherso constructed as toprovide for an electrical contact surface of maximum effective area.

A further object of the invention is to provide an electrode soconstructed as to eliminate likelihood of packing of the loose granularmaterial and likelihood of displacement of this material in any mannerliable to detract from the efficiency of the unit.

A further object of the invention is to evolve a novel method wherebythe electrode possessing the above-mentioned characteristics may beeconomically produced.

In the accompanying drawings:

Figure 1 is a perspective view illustrating the button or mount of theelectrode in its initial condition;

Figure 2 is a diametric section there through One of the-primary objectsof the Figure 3 is a. view similar touF igure; 1; illustrating the firststep in the preferred). method of constructing the electrode;

Figure 4 is a diametrie section through: the: electrode at thecompletion of the step, illustrated. in Figure 3;

Figure 5 is a view similar to Figure 4' illustrating the next step inthe method;

Figure 6 is a perspective view of the com pleted electrode;

Figure 7v is a diametric sectional view through the completed electrode;

Figure 8 is a" perspective viewvillustrating:

a slightly different method;

Figure 9 is a diametric section-through an electrode completed inaccordance with: the step illustrated invFigure- 8.

The drawings illustrate two forms of electrode anddisclose-two methods:of pro: ducing such an element.

Theelectrode embodying the invention consists essentially of" a cuppedbutton which is indicated in general by the numeral 1 and whichcomprisesa circular disk 2Jof any metal or composition: of metatls found suitableforthepurpose and-providedwith an upstanding peripheral flange so thatthe face of the button is: provided with a: shallow cavity 4; A.threadedshank 5 is provided upon the opposite faceof' the dislr 2 andafi'ords meanswhereby the disk or button may be mounted in the usualmanner. At this point it may be stated" that n 'hile: the button in theillustrated embodiment of the invention is in theform ofa flatcirculardisk, the principles of; the invention are applicable to electrodeshaving various other shapes and constructed in various other forms.- Thefirst step in the method' for producing the electrodes shown in Figures6 and 7 is illustrated in Figures 3 and 4 and consists in roughening thesurface of the disk 2 from which the flange 3 projects and as indicatedby the numeral 6, this being done in any convenient manner as forexample by the use of a sand blast although this surface might be etchedby acid or in fact roughened in any other manner found expedient. Afterthe disk has been roughsurfaced in the manner illustrated in Figand 4,there is introduced into the ures a cavity l, and preferably uniformlyspread, a thin layer 7 of a cementing or bonding material. Variousmaterials may be employed for this purpose and the invention is not infact limited to any particular material. For example use may be made ofdry shellac, the various jewelers cements. baking japans, certainsealing waxes, cer tain kinds of glazes, or even certain metal alloys.Having supplied the layer 7 of the cementing or bonding material, aquantity of carbon granules indicated by the numeral 8 is applied ordeposited within the cavity, the granules being spread or arranged asevenly as possible over the layer Y as best shown in Figure 5. Pressureis then applied to the layer of granules, and simultaneously, theassemblage is subjected to heat at a sufliciently high temperature tomelt or fuse the cementing or bonding material 7, whereupon, by reasonof the application of pressure, the granules 8 will be forced firmlyinto contact with the roughened surface 6 of the disk 9., and the entiremass of granules will be brought to a substantially level surface at thetop of the cavity at. Upon permitting the assemblage to cool, thecementing or bonding materials 7 will harden, and the carbon granuleswill become firmly and securely embedded therein and in electricalcontact with the roughened surface of the disk 2, the article in itscompleted form being shown in Figures 6 and 7. Carbon is preferably thegranular sub stance employed and it is th s material that is likewiseused in loose form in electrical contact with the electrode in thecompleted variable resistance unit as established in a microphonictransmitter. By roughening the surface of the disk the carbon particlesor granules 8 are brought into more intimate contact therewith, andlikewise a more firm or secure union is effected by the component partsof the electrode than would be the case if this surface were smoothlyfinished.

In that embodiment of the invention illustrated in Figures 8 and 9 ofthe drawings, instead of roughening the surface of the disk 2, acircular disk or sheet 9 of fine metal gauze may be arranged within thecavity 4 of the button 1 and serves the same purpose as the roughenedsurface 6 of the disk comprising the button, it being understood thatthe method of procedure is otherwise the same as above described.

From the foregoing description of the invention it will be evident thatthe contact surface of an electrode constructed in accordance with theinvention is of a rough or irregular contour as distinguished from thesmooth contact surface of the metal or carbon electrodes heretoforeemployed and that thus there is a more intimate electrical contactbetween the surface and the loose carbon particles, and also there is nolikelihood of the loose particles becoming compacted.

By providing the cavity at in the face of the button 1 the granules 8are confined within the bounds of the periphery of the button and areprevented from being forced over the edge and weakening the bond betweenthe parts at this point. Also by this means the granules are preventedfrom being chipped off if the button is subjected to rough handlingprior to installation in the transmitter.

Having thus described the invention, what is claimed as new is:

1. The method of producing an electrode for a variable resistance unitwhich comprises distributing upon the surface of a conducting base alayer of cementing or bonding material, distributing upon said layer aquantity of conducting granules, and subjecting the assemblage to heatand pressure to embed the granules in the cementing or bonding materialin electrical contact. with the surface of the base.

2. The method of producing an electrode for a variable resistance unitwhich com prises preparing a conducting base with a roughened surface,distributing upon the surface a layer of cementing or bondng material,distributing upon the said layer a layer of conducting granules, andsubjecting the assemblage to heat and pressure to embed the granules inthe cei'nenting or bonding material in electrical contact with the saidsurface of the base.

In testimony whereof I aiiix my signature.

FRANK L. WHITAKER. 11.. a]

